The present invention relates to the fabrication of semiconductor devices and more particularly to a method for cleaning a semiconductor substrate after the formation of dry etch residues thereon.
The importance of minimizing contamination during semiconductor fabrication processes has been recognized since the early days of the industry. As semiconductor devices have become smaller and more complex, cleanliness requirements have become increasingly stringent, especially for devices with submicron critical dimensions, because the ability to reliably create multi-level metallization structures is increasingly vital. The importance of cleaning and conditioning steps during the device fabrication process is also emphasized because small-scale residues that may not have seriously affected the performance of devices with large geometries may result in disabling defects in submicron devices.
Dry etch processes play a key role in developing multi-level metallization structures on semiconductor substrates. The step of transferring the desired pattern from the photoresist into the substrate is often accomplished via a dry etch process. While dry etch processes are effective for selectively etching the substrate in only the areas not masked by photoresist, these processes have a tendency to leave behind residues on the substrate. Although these residues may serve a beneficial role during a dry etch process, they are undesirable after the completion of the dry etch process. In back end of the line processes, where both dielectrics, such as SiO2, and metals, such as Al or W, are present, the residues left behind by dry etch processes may include both organometallic and organosilicate species. These undesirable post-etch residues are often difficult to remove without damaging the desired substrate features.
Current methods for removing dry etch residues have met with only limited success. Traditional cleans involving aqueous acid solutions can not provide a general solution for removing these residues, as these processes are not suitable for processing in the presence of metal lines. Current strategies often involve treating substrates with solutions containing hydroxylamine (NH2OH) and an organic chelating agent. These methods have shown some effectiveness but have significant drawbacks. These types of solutions can cause corrosion of exposed metal on the wafer and usually require long processing times at temperatures near 100 C. These hydroxylamine solutions are also expensive, as the chemicals are not only expensive to purchase but also typically require specialized disposal.
As the removal of dry etch residues grows increasingly troublesome in microelectronic device manufacture, there is a need for an effective method of removal of these residues which can be easily implemented in standard wafer processing equipment and has reduced costs for chemical purchase and disposal.
The present invention provides an adaptable method for removing organometallic, organosilicate, and other residues from a semiconductor substrate following a dry etch process. A substrate previously subjected to a dry etch process is exposed to a conditioning solution to remove residues remaining after the dry etch. The composition of the conditioning solution can be varied to match specific applications. The conditioning solution generally contains a source of fluorine, a complementary acid, a non-aqueous solvent, and preferably a surface passivation agent. One group of preferred conditioning solutions are solutions composed of HF, H3PO4, a polyhydric alcohol such as propylene glycol, and a surface passivation agent such as citric acid. In an alternate group of preferred embodiments the conditioning solutions are composed of HF, HCl, a polyhydric alcohol, and a surface passivation agent. The substrate is exposed to the conditioning solution for a sufficient amount of time to remove the undesired residues. After exposing the substrate to the conditioning solution, the substrate is rinsed, preferably by exposing the substrate to a rinse bath of a mildly acidic aqueous solution. Preferably this rinse step also involves bubbling a gas through the rinse bath to agitate the rinse bath.
Additional advantages and features of the present invention will be apparent from the following detailed description and drawings which illustrate preferred embodiments of the invention.